This disclosure pertains to processes of making pigment press cakes and using the pigment press cakes in preparing aqueous pigment dispersions. The dispersions thus obtained may be used in the preparation of aqueous ink-jet inks, pigmented paints, and the like. More particularly, this disclosure relates to a process of making pigment press cakes by coating pigments with polyetheramines using a grinding process.
Aqueous dispersions of pigments are widely used in ink-jet printing. Because a pigment is typically not soluble in an aqueous vehicle, it is often required to use a dispersing agent, such as a polymeric dispersant or a surfactant, to produce a stable dispersion of the pigment in the aqueous vehicle.
The use of dispersing agents, however, increases the viscosity of the dispersion over what it would be without the dispersing agents. Certain end use application of the dispersion, such as ink-jet ink, may have limitations on viscosity, thus having dispersing agents in a dispersion may reduce the formulation latitude of the dispersion for final products.
The use of self-dispersing pigment has been known in the art for many years. U.S. Pat. No. 2,439,442 discloses a process in which a carbon black pigment is exothermically reacted with a water solution of sodium hypochlorite, or is subjected to electrolysis in a sodium chloride solution, or is suspended in a sodium hydroxide solution and treated with chlorine gas to alter the colloidal properties such that the carbon black will readily and spontaneously disperse in water. U.S. Pat. No. 6,852,156 discloses a process of oxidizing carbon black using ozone under a dispersive environment. U.S. Pat. No. 6,120,594 discloses the oxidation of carbon black with hydrogen peroxide. U.S. Pat. No. 6,471,764 discloses the treatment of pigments with certain etheramine dispersing salts. U.S. Pat. No. 6,926,768 discloses treatment of organic pigments with certain etheramine salts.
While there are many approaches focusing on modifying the pigment surface by chemical reactions leading to hydrophilic moieties covalently attached to the pigment surface, organic color pigments such as quinacridone magenta, cyan and yellow are inherently difficult to treat and functionalize by chemical processing to produce a pigment that is readily dispersible in an aqueous vehicle.
A need exists for an effective, easy-to-operate, and lower cost process for making stable pigment dispersions containing organic color pigments as colorant. The present disclosure satisfies this need by providing a process for making a pigment dispersion by using a pigment press cake prepared from a coating process to entrap a hydrophilic polyetheramine to the surface of a pigment and thus facilitate the interaction between the pigment and a dispersant resulting in a stable pigment dispersion.